a) Field of the Invention
The invention is directed to an afocal zoom system, particularly for use in microscopes, comprising at least four optical component groups or assemblies, two of which are movable relative to one another and relative to the rest of the assemblies for purposes of changing magnification.
b) Description of the Related Art
Afocal zoom systems are known per se. They are used for the purposes changing magnification in conventional microscopes as one-channel systems or in stereo microscopes and surgical microscopes in two-channel construction according to the type of telescope. In contrast to Greenough type stereo microscopes using two objectives and two separate microscope beam paths which are inclined relative to one another at an angle of 12° to 14°, the telescope type is an embodiment form that is outfitted with a main objective common to both beam paths, the object lying in the object-side focal plane of the main objective. In this case, two partial bundles which are parallel to one another are cut out of the parallel light bundles offered by the objective in such a way that their axes which converge in front of the objective form the required angle of 12° to 14° and generate two real intermediate images considered at this angle.
Because of their limiting structural constraints, afocal zoom systems differ from photographic, video and telescopic systems and must therefore be classed in a special field of technology. In particular, the limited permissible lens diameter in two-channel constructions does not allow existing zoom systems already used in the fields and product groups mentioned above to be transferred to microscopy.
Afocal zoom systems with four optical assemblies and a zoom factor greater than 8 are often used in microscopes. Systems such as these are described, for example, in DE 202 07 780 U1, U.S. Pat. No. 6,320,702 B1, U.S. Pat. No. 6,157,495 and U.S. Pat. No. 6,335,833 B1.
Considered from the object, the systems indicated in these references are similarly formed of a stationary first group with positive refractive power, a movable second group with negative refractive power, a movable third group with positive refractive power, and a stationary fourth group with negative refractive power. The two middle groups are moved in opposite directions relative to one another in order to change the magnification. The magnification decreases when the distance between the two movable groups is increased.
All of the prior art publications cited above relate to this basic construction and this movement characteristic of the two movable assemblies.
Most of the space available for the entire zoom system is claimed by the movement areas of the movable assemblies. For example, the movement range in the zoom system according to U.S. Pat. No. 6,335,833 B1 is about 102 mm, while the overall length of the system and, therefore, the installed dimension, is about 150 mm.
This has the disadvantage that a space-saving construction of the components required for guiding the movable optical assemblies is not possible, which prevents a reduction of the structural dimensions of the microscopes. This applies particularly to microscopes in which the zoom system and the associated drive unit may not exceed predetermined dimensions.